Phil, thanks for the welcome! How would the 9mm perform against say a windshield of a vehicle? I'm not sure if you can answer that as its not a common situation but none the less.
Now that is a very good question and you're correct, I don't have a solid answer.
Here's my best understanding. The 9mm got a reputation of not being able to penetrate auto glass very well. I think tests have shown that is not true, it will penetrate fine but it depends on the angle it hits at. If it hits at an angle it can skip off. I believe there are 2 contributors to this, low mass and bullet shape, both of which the .40sw solve. Both can be reduced for the 9mm as well though. There are rounds available up to 147gr. with different shaped tips. My personal favorite round for 9mm is the 124gr Flat Point plated bullet. Haven't tried it against auto glass but it seems to be an 'all around' solid performer. My best guess (and it's a guess) is that the self defense rounds would also be effective at penetrating the auto glass, they may not be as effective at what's behind it though (depending on how much energy is left over).
With a little luck, there may be someone on here who's actually done some tests.